Field of the Invention
The invention relates to a turbine shaft which is aligned along a principal axis and includes an inflow region for fluid, and at least two mutually spaced recesses adjoining the inflow region in axial direction for receiving at least one turbine blade in each case. The invention furthermore relates to a steam turbine and a method for cooling an inflow region of a turbine shaft disposed in a turbine, in particular a steam turbine.
German Published, Non-Prosecuted Patent Application DE 32 09 506 A1, corresponding to U.S. Pat. No. 4,571,153, relates to an axial-flow steam turbine, especially one of double-flow construction. In a steam inflow region, an annular passage is formed between the shaft and an annular shaft shield. The shaft has a rotationally symmetrical depression in the steam inflow region. The annular shaft shield projects partially into the depression and is connected to the casing of the turbine through first fixed-blade rows and supported thereby. The shaft shield has conduits for the purpose of introducing steam. The conduits are disposed centrally with respect to the inflow region, between the first fixed blades and they open tangentially into a gap between the rotating shaft and the fixed shield supported by the casing.
German Published, Non-Prosecuted Patent Application DE 34 06 071 A1 discloses an annular shaft shield which is disposed between two rings of the first fixed-blade rows. The shaft shield shields the outer periphery or surface of the turbine shaft from the live steam. The shaft shield has inlets upstream of the rings through which a partial stream of the live steam passes in a restricted manner into a gap between the shaft shield and the turbine shaft. The inlets are angled in such a way that the live steam has a flow component imparted to it in the circumferential direction of the turbine shaft. Auxiliary fixed blades and auxiliary rotating blades can be respectively provided on the inner periphery of the shaft shield and the turbine shaft.
The use of steam at relatively high pressures and temperatures, especially in what are referred to as supercritical steam conditions, with a temperature of, for example, above 550.degree. C., contribute to an increase in the efficiency of a steam turbine. The use of steam in such a condition makes increased demands on a steam turbine that is acted upon in a corresponding manner, particularly on the turbine shaft of the steam turbine.
Patent Abstracts of Japan Publication No. JP 58/133402 describes a double-flow steam turbine which is provided with a chamber construction. Wheel discs which are mounted on the turbine shaft have turbine blades disposed on their respective outer ends. A cover plate disposed in the intermediate region of the turbine shaft into which the working fluid flows, is held by respective first stationary blade rows. The cover plate, which is disposed at the upper end of the wheel discs, forms a non-sealing end for a spatial region, which on one hand is formed by the sides of the wheel discs and on the other hand by the turbine shaft. The wheel discs defining the spatial region have openings for the inflow of working fluid into the spatial region. The openings are sized differently, so that a vacuum is generated in the spatial region and working fluid can flow into the spatial region at least through one wheel disc.